The present invention relates to a photocathode and an electron tube.
An electron tube is a device for detecting faint light using a photocathode that emits electrons in response to incident light. Examples of electron tubes include a photomultiplier tube, a streak tube, and an image intensifier. Japanese patent application publication 8-255580 discloses an electron tube having a field-assisted photocathode as an electron tube having sensitivity to longer wavelength light. In this photocathode, a bias voltage is applied between both surfaces of the photocathode, causing electrons to be accelerated by the electric field generated in the photocathode plate and emitted into a vacuum. In this construction, the photocathode is attached to a body of the electron tube by adhesive.
However, the following problems arise in conventional electron tubes one of the problems is that the photocathode is easily peeled off due to thermal stress generated by vibrations and/or temperature variations near 100xc2x0 C. occurring when the electron tube is cooled for use at about xe2x88x9270xc2x0 C. The photocathode does not achieve sufficient strength, because the photocathode is adhered to the electron tube using an adhesive. Another problem arises when gas generated from the adhesive degrades the degree of vacuum in the electron tube.
In view of the foregoing, it is an object of the present invention to provide a photocathode in which a photocathode can be reliably fixed without using adhesive, and an electron tube equipped with the above photocathode.
The photocathode according to the present invention includes a faceplate having a light incident surface on which light is incident and a light transmissive surface through which the incident light is transmitted; a photocathode plate in contact with the light transmissive surface of the faceplate for emitting electrons from an electron emitting surface disposed on the opposite side of the surface of contact with the light transmissive surface in response to incident light; a first pin embedded in the faceplate and extending between the light incident surface of the faceplate and the portion of the light transmissive surface that does not contact the photocathode plate; and a support plate joined to the first pin on the light transmissive surface and contacting the outer edge of the electron emitting surface of the photocathode plate to fix the photocathode plate to the faceplate.
With this photocathode construction, the photocathode plate can be easily and reliably fixed to the faceplate without using adhesive. Particularly, the photocathode plate can be joined to the faceplate using metallic first pin and a metallic support plate by welding or soldering the metallic first pin to the metallic support plate.
Here, preferably, a voltage is applied to the photocathode plate through the first pin and the support plate. Accordingly, wiring on the light transmissive surface for applying a voltage to the light transmissive surface of the faceplate is not necessary.
Preferably, the photocathode can be provided with a second pin formed from metal and embedded in the faceplate. The second pin is positioned between the light incident surface and the portion of the light transmissive surface contacting the photocathode plate to be electrically connected to the photocathode plate. A voltage can be applied to the photocathode plate via the second pin. With this construction, wiring on the light transmissive surface for applying voltages to the light transmissive surface side of the faceplate is not necessary.
Further, a bias voltage can be applied between both surfaces of the photocathode plate. Accordingly, a field-assisted type photocathode plate can be easily and reliably fixed to the faceplate without using adhesive.
Preferably, the photocathode can be provided with a second pin formed from metal and embedded in the faceplate. The second pin extends between the light incident surface and a portion of the light transmissive surface contacting the photocathode plate to be electrically connected to the photocathode plate. One end of a bias voltage source can be connected to the photocathode plate via the second pin. With this construction, wiring on the light transmissive surface for applying a bias voltage to the light transmissive surface side of the faceplate is not necessary.
Preferably, one end of a bias voltage source can be connected to the photocathode plate via the first pin and the support plate. With this construction, wiring on the light transmissive surface for applying a bias voltage to the light transmissive surface side of the faceplate is not necessary.
Preferably, the photocathode can, be provided with a second pin formed from metal and embedded in the faceplate. The second pin extending between the light incident surface and a portion of the light transmissive surface contacting the photocathode plate to be electrically connected to the photocathode plate. Preferably, the other end of the bias voltage source is connected to the photocathode plate via the second pin. With this construction, wiring on the light transmissive surface for applying the bias voltages between both sides of the faceplate is not necessary.
When the support plate is formed from metal, it is preferable to provide an insulating holder around the photocathode plate. With this construction, in case that the photocathode plate is moved for any reason toward the support plate, the insulating holder can prevent short-circuit between a side surface of the photocathode plate and the support plate.
Preferably, the photocathode plate can include a plurality of first pins. This structure enables the photocathode plate to be more reliably fixed to the faceplate.
Preferably, the second pin can be electrically connected to the photocathode plate via a conductive member. With this construction, the conductive member serves as an electrode to efficiently apply a voltage to the photocathode plate.
Further, the faceplate exhibits sufficient functions, provided only the portion of the faceplate that guides light onto the photocathode plate is formed from a light transmissive member.
Further, the support plate is a flat plate having a stepped through-hole. The stepped through-hole can have a rim portion which contacts an outer edge of the electron emitting surface in the photocathode plate to fix the photocathode plate to the faceplate. This construction facilitates production of the photocathode.
The usage of the above photocathode plate can provide an electron tube such as an image intensifier, streak tube, or photomultiplier tube. And the electron tube exhibits sufficiently proper characteristics.